Injection molding is a well-known process for producing parts from both thermoplastic and thermosetting plastic materials. In the process, plastic material is fed into a heated barrel to become molten, mixed, and then forced under pressure via flow paths into a mold cavity whose shape complements the shape of the final part. Afterwards, the cavity is cooled causing the plastic to harden as the final part. The mold is then opened, and the part removed along with any hardened plastic that may remain in the flow channels upstream of the part cavity.
Molding architectures generally involve the use of a series of mating plates for delivering and distributing the molten plastic to one or more cavities. The plates are held together against one another by a hydraulic clamping arrangement during the molding cycle. The clamping arrangement typically utilizes a fixed plate on one end of the mold plate stack and a moveable plate that travels between open and closed positions during the mold cycle. The amount of force required to maintain mold plates in contact with one another during the injection portion of the cycle is referred to as the clamping force and can be considerable, usually measured in tons.
In many molding architectures, melt flows in a more or less straight line from the injector nozzle to the gate of the part cavity. In such in-line configurations, use is often made of a valve gate pin to open and close the cavity gate to regulate flow into the cavity.
Various methods and mechanisms of varying complexity have been used to selectively control the actuation of in-line valve gate pins. All require the application of considerable force to the pin for proper control of the gate. In addition, any design must manage the thermal environment of the mold architecture and be sensitive to the possibility of deleterious effects caused by the presence of high heat generated by components along the flow path, including heat sources found in the various plates typically employed.
In many instances, use has been made of pneumatic reciprocating pistons to move the pin between open and closed positions. Such approaches have placed mechanisms proximate the in-line flow path, more or less residing within the plate arrangement, thus resulting in complex architectures and heat management concerns.
For example, use has been made of small pistons whose sealing O-rings are in direct contact with heated flow steel. In another approach, a piston was placed in the top clamp plate to keep it more or less cool by placing it remotely from down stream heaters. Another approach placed the entire actuating mechanism above the locating ring and employed a small piston, but subjected O-rings to deleterious heat.
Other approaches have located the actuating mechanism out of the direct in-line flow path. For example, external pistons have been used to drive a cam to move the pin. Another has the piston displaced with respect to the in-line path using a rocker arm extending into the in-line path to move the pin. Another out of line approach used a motor driven spline shaft to drive a rack in the pin.
While many approaches have been used for in-line valve gate actuators, a need still exists for a solution that addresses various unsolved problems.
Consequently, it is a principle object of this invention to provide improved in-line valve gate pin actuation.
It is still another object of the present invention to provide high pin force for in-line valve gate actuation.
It is yet another object of the present invention to provide in-line valve gate actuation mechanisms that are compact, simple, and reliable.
It is another object of the present invention to provide in-line valve gate actuators that can process most highly filled and unfilled commodity resins.
It is yet another object of the present invention to provide a pneumatic actuating cylinder within an integrated mold locating ring to lessen deleterious thermal effects on piston seals.
It is still another object of the present invention to provide valve gate actuators that move with in-line action to reduce wear.
It is yet another object of the present invention to provide in-line valve gate actuation with the ability to easily change nozzles to accommodate a variety of applications.
Other objects of the invention will, in part, be obvious, and will, in part, appear hereinafter when the following detailed description is read in connection with the accompanying drawings.